Support is requested for a Keystone Symposia meeting entitled Positive Strand RNA Viruses, organized by Eric J. Snijder and Ralf Bartenschlager. The meeting will be held in Boston, Massachusetts from April 28 - May 3, 2013. The general topic of this meeting is relevant to the NIAID mission with respect to the broad area of viral pathogen research. Originally initiated in 1986 as a Keystone Symposia meeting, and later continued by Dr. Margo Brinton as primary organizer for more than 25 years, the triennial international symposium on Positive Strand RNA Viruses has provided an international forum for recent research on human, animal, plant, insect, and bacterial viruses with positive-strand RNA genomes. These pathogens constitute the largest group of viral agents including a large number of important human pathogens like hepatitis C virus, West Nile and dengue viruses, hepatitis A virus and poliovirus. Furthermore, the enormous variety of positive-stranded RNA viruses found in animals, and their evolutionary potential, continues to pose a threat of novel (zoonotic) infections emerging in human populations as illustrated by the emergence of the SARS coronavirus. The 2013 meeting on Positive Strand RNA Viruses, now back under the roof of Keystone Symposia, will cover both basic and applied research and provide an unparalleled platform to discuss the unique and common features of the members of this important virus group. Experienced and junior researchers will come together to discuss the latest developments in the areas of the molecular biology, pathogenesis, evolution and epidemiology of positive-stranded RNA viruses, aiming to translate these findings into novel approaches to diagnose and control infections by these agents.